Solar cells which include the use of certain poly(vinyl butyral)/film bilayer encapsulant layers with a low blocking tendency and a simplified process to produce thereof

ABSTRACT

The present invention provides a solar cell laminate comprising a preformed bi-layer sheet having a poly(vinyl butyral) sub-layer.

FIELD OF THE INVENTION

The present invention relates to solar cell modules comprising anon-blocking poly(vinyl butyral) containing bi-layer sheet.

BACKGROUND OF THE INVENTION

As a renewable energy resource, the use of solar cell modules is rapidlyexpanding. With increasingly complex solar cell modules or laminates,also referred to as photovoltaic modules, comes an increased demand forenhanced functional encapsulant materials. Photovoltaic (solar) cellmodules or laminates are units that convert light energy into electricalenergy. Typical or conventional construction of a solar cell laminateconsists of at least 5 structural layers. The layers of a conventionalsolar cell module are constructed in the following order starting fromthe top, or incident layer (that is, the layer first contacted by light)and continuing to the backing (the layer furthest removed from theincident layer): (1) incident layer or front-sheet, (2) front-sheet (orfirst) encapsulant layer, (3) voltage-generating layer (or solar celllayer), (4) back-sheet (second) encapsulant layer, and (5) backing layeror back-sheet. The function of the incident layer is to provide atransparent protective window that will allow sunlight into the solarcell module. The incident layer is typically a glass plate or a thinpolymeric film (such as a fluoropolymer or polyester film), but couldconceivably be any material that is transparent to sunlight.

The encapsulant layers of solar cell laminates are designed toencapsulate and protect the fragile voltage-generating layer. Generally,a solar cell laminate will incorporate at least two encapsulant layerssandwiched around the solar cell layer. The optical properties of thefront-sheet encapsulant layer must be such that light can be effectivelytransmitted to the solar cell layer. Over the years, a wide variety ofpolymeric films and sheets have been developed to produce laminatedsolar cell products. In general, these polymeric films and sheets mustpossess a combination of characteristics including very high opticalclarity, low haze, high impact resistance, shock absorbance, excellentultraviolet light resistance, good long term thermal stability,excellent adhesion to glass and other solar cell laminate layers, lowultraviolet light transmittance, low moisture absorption, high moistureresistance, excellent long term weatherability, among otherrequirements. Widely used encapsulant materials utilized currentlyinclude complex, multi-component compositions based on ethylene vinylacetate (EVA), ionomer, poly(vinyl butyral) (PVB), polyurethane (PU),polyvinylchloride (PVC), metallocene-catalyzed linear low densitypolyethylenes, polyolefin block elastomers, ethylene acrylate estercopolymers, such as poly(ethylene-co-methyl acrylate) andpoly(ethylene-co-butyl acrylate), acid copolymers, silicone elastomers,epoxy resins, and the like.

Ethylene vinyl acetate compositions, which have commonly been utilizedas the encapsulant layer within solar cell modules, suffer theshortcomings of low adhesion to the other components used in the solarcell module, low creep resistance during the lamination process andend-use and low weathering and light stability. These shortcomings havegenerally been overcome through the formulation of adhesion primers,peroxide curing agents, and thermal and UV stabilizer packages into theethylene vinyl acetate compositions, which necessarily complicates thesheet production and ensuing lamination processes.

Poly(vinyl butyral) compositions have also been commonly disclosed asencapsulant layers for solar cell modules. For example, Baskett, et.al., in U.S. Pat. No. 3,957,537, disclose the use of poly(vinyl butyral)as a hot melt adhesive in the production of solar cells. Furtherexamples of the use of poly(vinyl butyral) in solar cell encapsulantlayers include U.S. Pat. Nos. 4,249,958; 4,321,418; 5,508,205;5,582,653; 5,728,230; 6,075,202; 6,288,323; 6,288,326; 6,538,192;6,777,610; 6,822,157; 6,940,008, U.S. Patent Application Nos.2004/0191422 and 2005/0284516, European Patent Nos. EP 0 343 628; EP 0631 328; EP 1 005 096; and EP 1 054 456.

However, due to the extreme softness and tackiness at ambienttemperature, the use of poly(vinyl butyral) sheets within solar cellmodules has been complicated by the need to refrigerate the poly(vinylbutyral) sheet during shipment and storage. In addition, plasticizedpoly(vinyl butyral) films, wherein the tackiness augments with risingtemperature and the sliding property towards glass gets worse, have atendency to impair processability and workability. In order to improvethe tendency and to suppress the hygroscopy, the temperature of theworking places must be maintained at about 20° C. In practice, when aplasticized poly(vinyl butyral) film is used as the intermediate layerbetween two sheets of glass, it is necessary to adopt a two-step bondingprocess to prepare the laminate (see e.g., European Patent No. EP 0 145928, page 2, line 30).

Bi-layer laminates comprising a poly(vinyl butyral) sub-layer have beenused in the glazing art and are commercially available under the tradename SentryGlas® SpallShield by the E. I. du Pont de Nemours and Company(DuPont), Wilmington, Del. These bi-layer laminates are generallyapplied directly to a glass surface to produce vandal and burglaryresistant glass, more particularly to prevent spalling, which is theshower of razor-sharp glass pieces which occurs opposite the side ofimpact when a glass pane, especially a tempered glass pane, is broken.Glazings which include such structures are disclosed in, for example,U.S. Pat. Nos. 3,781,184; 3,900,673; 4,059,469; 4,072,779; 4,242,403;4,469,743; 4,543,283; 4,832,782; 4,834,829; 4,925,737; 4,952,457;5,028,287; 5,069,942; 5,082,515; 5,188,692; 5,250,146; 5,356,745;5,393,365; 5,415,942; 5,501,910; 5,567,529; 5,631,089; 5,698,053;5,763,089; 5,965,853, and U.S. Patent Application No. 2005/0129954.

The present invention provides a solar cell laminate comprising apreformed poly(vinyl butyral)/film bi-layer sheet and a simplifiedprocess for producing the same. By “preformed”, it is meant that the twosub-layers of the bi-layer sheet have been laminated and bonded togetherto form a single unit prior to any further process involving thebi-layer sheet in the construction of a solar cell laminate structure.Specifically, during a conventional process, when poly(vinyl butyral)sheets are used as laminate layers, interleave layers, e.g.,polyethylene or polypropylene film layers, are often used during thelamination process and then discarded as undesirable waste. In thepresent invention, however, the film sub-layer of the preformed bi-layersheet serves as an interleave layer to the poly(vinyl butyral) sheet,and, instead of being discarded, the film sub-layer remains in thelaminate providing additional function(s).

SUMMARY OF THE INVENTION

In one aspect, the present invention is a solar cell laminate comprising(i) a solar cell layer comprising one or a plurality of electronicallyinterconnected solar cells and having a light-receiving side and a backside, and (ii) at least one preformed bi-layer sheet comprising a firstsub-layer comprising a poly(vinyl butyral) and a second sub-layercomprising a metal or polymeric film, wherein the preformed bi-layersheet is at either the light-receiving side or the back side of thesolar cell laminate.

In one particular embodiment, the at least one preformed bi-layer sheetis laminated to the light-receiving side of the solar cell layer andserves as a front-sheet encapsulant layer, and the second sub-layer ofthe at least one preformed bi-layer sheet comprises the polymeric film.

In another embodiment, the solar cell laminate further comprises aback-sheet encapsulant layer laminated to the back side of the solarcell layer and it is preferred that the back-sheet encapsulant layer isalso formed of a preformed bi-layer sheet, wherein the second sub-layermay be a metal or polymeric film.

In yet another embodiment, the at least one preformed bi-layer sheet islaminated to the back side of said solar cell layer and serves as aback-sheet encapsulant layer. And preferably, the solar cell laminatefurther comprises a front-sheet encapsulant layer laminated to thelight-receiving side of the solar cell layer.

In yet another embodiment, the solar cell laminates may furthercomprising an incident layer, and/or a back-sheet, and/or additionalencapsulant layers, wherein the additional encapsulant layers areincluded to bind the second sub-layer of the preformed bi-layer sheetwith other laminate layers.

In another aspect, the present invention is a process of manufacturing asolar cell laminate comprising: (i) providing an assembly comprising,from top to bottom, a front-sheet encapsulant layer, a solar cell layercomprising one or a plurality of electronically interconnected solarcells, and a back-sheet encapsulant layer, and (ii) laminating theassembly to form the solar cell module, wherein at least one of the twoencapsulant layers is formed of a preformed bi-layer sheet comprising afirst sub-layer comprising a poly(vinyl butyral) and a second sub-layercomprising a metal or polymeric film. Preferably, the lamination isconducted by subjecting the assembly to heat and pressure or vacuum.

In one particular embodiment, the front-sheet encapsulant layer in theassembly is formed of the preformed bi-layer sheet with its firstsub-layer in direct contact with the solar cell layer, and the assemblyfurther comprises a back-sheet placed next to the back-sheet encapsulantlayer opposite from the solar cell layer. The assembly may furthercomprise a second front-sheet encapsulant layer and an incident layer,wherein the incident layer is placed next to the second front-sheetencapsulant layer, which in turn is in direct contact with the secondsub-layer of the preformed bi-layer sheet.

In yet another embodiment, the back-sheet encapsulant layer in theassembly is formed of the preformed bi-layer sheet with its firstsub-layer in direct contact with the solar cell layer, and the assemblyfurther comprises an incident layer placed next to the front-sheetencapsulant layer opposite from said solar cell layer. The assembly mayfurther comprise a second back-sheet encapsulant layer and a back-sheet,wherein the back-sheet is placed next to said second back-sheetencapsulant layer, which in turn is in direct contact with the secondsub-layer of said preformed bi-layer sheet.

In yet another embodiment, the front-sheet encapsulant layer in theassembly is formed of the preformed bi-layer sheet with its secondsub-layer in a closer proximity to the solar cell layer, and theassembly further comprises an incident layer, a second front-sheetencapsulant layer, and a back-sheet, wherein the incident layer isplaced next to the first sub-layer of the preformed bi-layer sheet,which in turn has its second sub-layer in direct contact with the secondfront-sheet encapsulant layer, and which in turn is in direct contactwith the solar cell layer; and wherein the back-sheet is placed next tothe back-sheet encapsulant layer opposite from said solar cell layer.

In yet another embodiment, the back-sheet encapsulant layer in theassembly is formed of the preformed bi-layer sheet with its secondsub-layer in a closer proximity to the solar cell layer, and theassembly further comprises an incident layer, a second back-sheetencapsulant layer, and a back-sheet, wherein the incident layer isplaced next to the front-sheet encapsulant layer opposite from the solarcell layer, and wherein the back-sheet is placed next to the firstsub-layer of the preformed bi-layer sheet, which in turn has its secondsub-layer in direct contact with the second back-sheet encapsulantlayer, and which in turn is in direct contact with the solar cell layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a preformed bi-layer sheet 10disclosed herein. The preformed bi-layer sheet 10 comprises a firstsub-layer 12 and a second sub-layer 14, wherein the first sub-layer 12comprises a poly(vinyl butyral) and the second sub-layer 14 is formed ofa metal or polymeric film.

FIG. 2 is a cross-sectional view of a typical prior art solar cellmodule 20 comprising (i) an incident layer 21, (ii) a front-sheetencapsulant layer 22, (iii) a solar cell layer 23, (iv) a back-sheetencapsulant layer 24, and (v) a back-sheet 25.

FIG. 3 is a cross-sectional view of one particular embodiment of thepresent invention, wherein solar cell module 20 a comprises one layer ofthe preformed bi-layer sheet 10 in which the first sub-layer 12 is indirect contact with the light-receiving side 23 a of solar cell layer23. In this embodiment, the preformed bi-layer sheet 10 may serve asboth a front-sheet encapsulant layer 22 and an incident layer 21.

FIG. 4 is a cross-sectional view of another embodiment of the presentinvention, wherein, compare to solar cell laminate 20 a in FIG. 3,laminate 20 b further comprises an incident layer 21 laminated next to asecond front-sheet encapsulant layer 22 a, which in turn is laminatednext to the second sub-layer 14 of the preformed bi-layer sheet 10.

FIG. 5 is a cross-sectional view of yet another embodiment of thepresent invention, wherein solar cell module 20 c comprises one layer ofthe preformed bi-layer sheet 10 in which the first sub-layer 12 is indirect contact with the back side 23 b of solar cell layer 23. In thisembodiment, the preformed bi-layer sheet 10 may serve as both aback-sheet encapsulant layer 24 and a back-sheet 25.

FIG. 6 is a cross-sectional view of yet another embodiment of thepresent invention, wherein, compare to solar cell laminate 20 c in FIG.5, laminate 20 d further comprises a back-sheet 25 laminated next to asecond back-sheet encapsulant layer 24 a, which in turn is laminatednext to the second sub-layer 14 of the preformed bi-layer sheet 10.

FIG. 7 is a cross sectional view of yet another embodiment of thepresent invention, wherein the solar cell module 20 e comprises a firstpreformed bi-layer sheet 10 having its first sub-layer 12 in directcontact with the light-receiving side 23 a of solar cell layer 23 and asecond preformed bi-layer sheet 10 having its first sub-layer 12 indirect contact with the back side 23 b of solar cell layer 23. In thisembodiment, the first preformed bi-layer sheet 10 may serve as both afront-sheet encapsulant layer 22 and an incident layer 21, and thesecond preformed bi-layer sheet 10 may serve as both a back-sheetencapsulant layer 24 and a back-sheet 25.

FIG. 8 is a cross sectional view of yet another embodiment of thepresent invention, wherein solar cell module 20 f comprises one layer ofthe preformed bi-layer sheet 10 in which the second sub-layer 14 is in acloser proximity to the light-receiving side 23 a of solar cell layer23. In addition, solar cell module 20 f further comprises a secondfront-sheet encapsulant layer 22 a which is placed in between thepreformed bi-layer sheet 10 and an incident layer 21.

FIG. 9 is a cross sectional view of yet another embodiment of thepresent invention, wherein solar cell module 20 g comprises one layer ofthe preformed bi-layer sheet 10 in which the second sub-layer 14 is in acloser proximity to the back side 23 b of solar cell layer 23. Inaddition, solar cell module 20 g further comprises second back-sheetencapsulant layer 24 a which is placed in between the preformed bi-layersheet 10 and a back-sheet 25.

DETAILED DESCRIPTION OF THE INVENTION

To the extent permitted by the United States law, all publications,patent applications, patents, and other references mentioned herein areincorporated by reference in their entirety.

The materials, methods, and examples herein are illustrative only andthe scope of the present invention should be judged only by the claims.

Definitions

The following definitions apply to the terms as used throughout thisspecification, unless otherwise limited in specific instances.

Unless stated otherwise, all percentages, parts, ratios, etc., are byweight.

When the term “about” is used in describing a value or an end-point of arange, the disclosure should be understood to include the specific valueor end-point referred to.

In the present application, the terms “sheet” and “film” are used intheir broad sense interchangeably.

In describing and/or claiming this invention, the term “copolymer” isused to refer to polymers containing two or more monomers.

When a first film or sheet is said to be “laminated to” a second film orsheet, it is meant that the first film or sheet is laminated to thesecond film or sheet directly or indirectly. By directly, it is meantthe first film or sheet is in direct contact with and adhered to thesecond film or sheet. By indirectly, it is meant that the first film orsheet is not in direct contact with the second film or sheet, rather, itis bonded to the second film or sheet by at least one additional layerof film or sheet that is placed in between.

Bi-Layer Sheets

Now referring to FIG. 1, the present invention relates to the use of atleast one preformed bi-layer sheet 10 in a solar cell module orlaminate. The preformed bi-layer sheet 10 has a first sub-layer 12derived from a poly(vinyl butyral) sheet and a second sub-layer 14derived from a metal or polymeric film.

I. Poly(vinyl butyral) Sheets

In accordance to the present invention, the poly(vinyl butyral) sheetsdisclosed herein are derived from certain poly(vinyl butyral)compositions. The poly(vinyl butyral) used herein may be produced byaqueous or solvent acetalization. In a solvent process, acetalization iscarried out in the presence of sufficient solvent to dissolve thepoly(vinyl butyral) and produce a homogeneous solution at the end ofacetalization. The poly(vinyl butyral) is separated from solution byprecipitation of solid particles with water, which are then washed anddried. Solvents used are lower aliphatic alcohols such as ethanol. In anaqueous process, acetalization is carried out by adding butyraldehyde toa water solution of poly(vinyl alcohol) at a temperature of about 20° C.to about 100° C., in the presence of an acid catalyst, agitating themixture to cause an intermediate poly(vinyl butyral) to precipitate infinely divided form and continuing the agitation while heating until thereaction mixture has proceeded to the desired end point, followed byneutralization of the catalyst, separation, stabilization and drying ofthe poly(vinyl butyral) resin. For example, poly(vinyl butyral) resincan be produced as disclosed within U.S. Pat. Nos. 3,153,009 and4,696,971.

The poly(vinyl butyral) used herein will typically have a weight averagemolecular weight from about 30,000 to about 600,000, or preferably, fromabout 45,000 to about 300,000, or more preferably, from about 200,000 to300,000, as measured by size exclusion chromatography using low anglelaser light scattering. Poly(vinyl butyral) compositions used herein maycomprise, on a weight basis, about 12% to about 23%, or preferably,about 14% to about 21%, or more preferably, about 15% to about 19.5%, ormost preferably, about 15% to about 19%, of hydroxyl groups calculatedas polyvinyl alcohol (PVOH). The hydroxyl number can be determinedaccording to standard methods, such as ASTM D1396-92. In addition, thepoly(vinyl butyral) compositions used herein may include 0 to about 10%,or preferably, 0 to about 3%, of residual ester groups, calculated aspolyvinyl ester, typically acetate groups, with the balance beingbutyraldehyde acetal. The poly(vinyl butyral) composition may alsocontain a minor amount of acetal groups other than butyral, e.g.,2-ethyl hexanal, as disclosed within U.S. Pat. No. 5,137,954.

The poly(vinyl butyral) composition used herein typically contains aplasticizer and the amount depends on the specific poly(vinyl butyral)resin and the properties desired in the application. The plasticizerprovides enhanced flexibility and processability of the poly(vinylbutyral) composition. Suitable plasticizers are commonly known withinthe art, e.g., as disclosed in U.S. Pat. Nos. 3,841,890; 4,144,217;4,276,351; 4,335,036; 4,902,464; 5,013,779 and PCT Patent ApplicationNo. WO 96/28504. Plasticizers commonly employed are esters of apolybasic acid or a polyhydric alcohol. Preferred plasticizers include,but are not limited to, diesters obtained by the reaction of triethyleneglycol or tetraethylene glycol with aliphatic carboxylic acids havingfrom 6 to 10 carbon atoms; diesters obtained from the reaction ofsebacic acid with aliphatic alcohols having from 1 to 18 carbon atoms;oligoethylene glycol di-2-ethylhexanoate; tetraethylene glycoldi-n-heptanoate; dihexyl adipate; dioctyl adipate; mixtures of heptyland nonyl adipates; dibutyl sebacate; tributoxyethylphosphate;isodecylphenylphosphate; triisopropylphosphite; polymeric plasticizers,such as, the oil-modified sebacid alkyds; mixtures of phosphates andadipates; mixtures of adipates and alkyl benzyl phthalates; and mixturesthereof. More preferred plasticizers include triethylene glycoldi-2-ethylhexanoate, tetraethylene glycol di-n-heptanoate, dibutylsebacate, and mixtures thereof. A single plasticizer can be used or amixture of plasticizers can be used. For convenience, when describingthe compositions of the present invention, a mixture of plasticizers canalso be referred to herein as “plasticizer”. That is, the singular formof the word “plasticizer” as used herein may represent the use of eitherone plasticizer or the use of a mixture of two or more plasticizers.

As described above, the plasticizer provides flexibility andprocessability to the poly(vinyl butyral) composition. Preferably, thepoly(vinyl butyral) compositions used herein incorporate about 15 toabout 60 wt %, or more preferably, about 15 to about 50 wt %, or mostpreferably, about 25 to about 40 wt %, of a plasticizer based on thetotal weight of the poly(vinyl butyral) composition.

The poly(vinyl butyral) compositions used herein also include acousticpoly(vinyl butyral) resins having, e.g., a single plasticizer in theamount in the range of from about 28 to about 40 wt %. Suitable acousticpoly(vinyl butyral) compositions are disclosed in PCT Patent ApplicationNo. WO 2004/039581.

An adhesion control additive for, e.g., controlling the adhesive bondbetween the poly(vinyl butyral) sub-layer and other component layers inthe solar cell laminates, may also be used. These are generally alkalimetal or alkaline earth metal salts of organic and inorganic acids.Preferably, they are alkali metal or alkaline earth metal salts oforganic carboxylic acids having from 2 to 16 carbon atoms. Morepreferably, they are magnesium or potassium salts of organic carboxylicacids having from 2 to 16 carbon atoms. Specific examples of theadhesion control additives used herein include, e.g., potassium acetate,potassium formate, potassium propanoate, potassium butanoate, potassiumpentanoate, potassium hexanoate, potassium 2-ethylbutylate, potassiumheptanoate, potassium octanoate, potassium 2-ethylhexanoate, magnesiumacetate, magnesium formate, magnesium propanoate, magnesium butanoate,magnesium pentanoate, magnesium hexanoate, magnesium 2-ethylbutylate,magnesium heptanoate, magnesium octanoate, magnesium 2-ethylhexanoateand the like and mixtures thereof. The adhesion control additive istypically used in the range of about 0.001 to about 0.5 wt % based onthe total weight of the polymeric sheet composition.

Surface tension controlling agents, such as Trans® 290 or Trans® 296(available from the Trans-Chemco Company) or Q-23183® (available fromthe Dow Chemical Company) can be used in the poly(vinyl butyral)compositions used herein.

The poly(vinyl butyral) compositions used herein may also contain otheradditives known within the art. The additives may include, but are notlimited to, plasticizers, processing aides, flow enhancing additives,lubricants, pigments, dyes, flame retardants, impact modifiers,nucleating agents to increase crystallinity, anti-blocking agents suchas silica, thermal stabilizers, UV absorbers, UV stabilizers,dispersants, surfactants, chelating agents, coupling agents, adhesives,primers, reinforcement additives, such as glass fiber, fillers and thelike. For example, typical colorants can include a bluing agent toreduce yellowing. Generally, additives that may reduce the opticalclarity of the composition, such as reinforcement additives and fillers,are reserved for those sheets used as back-sheet encapsulant layers orback-sheets.

The poly(vinyl butyral) compositions used herein may further contain aneffective amount of a thermal stabilizer. Thermal stabilizers arewell-known in the art. Any known thermal stabilizer may find utilitywithin the present invention. Preferable general classes of thermalstabilizers include, but are not limited to, phenolic antioxidants,alkylated monophenols, alkylthiomethylphenols, hydroquinones, alkylatedhydroquinones, tocopherols, hydroxylated thiodiphenyl ethers,alkylidenebisphenols, O-, N- and S-benzyl compounds, hydroxybenzylatedmalonates, aromatic hydroxybenzyl compounds, triazine compounds, aminicantioxidants, aryl amines, diaryl amines, polyaryl amines,acylaminophenols, oxamides, metal deactivators, phosphites,phosphonites, benzylphosphonates, ascorbic acid (vitamin C), compoundswhich destroy peroxide, hydroxylamines, nitrones, thiosynergists,benzofuranones, indolinones, and the like and mixtures thereof. Morepreferably, the thermal stabilizer is a bis-phenolic antioxidant, whichhave been found to be surprisingly suitable for preparing low colorpoly(vinyl butyral), especially when used in combination with thetriethylene glycol di-2-ethylhexanoate plasticizer. Suitable specificbis-phenolic antioxidants include2,2′-ethylidenebis(4,6-di-t-butylphenol);4,4′-butylidenebis(2-t-butyl-5-methylphenol);2,2′-isobutylidenebis(6-t-butyl-4-methylphenol); and2,2′-methylenebis(6-t-butyl-4-methylphenol). Bis-phenolic antioxidantsare commercially available under the tradename of Anox® 29, Lowinox®22M46, Lowinox® 44B25, and Lowinox® 221B46, for example. The poly(vinylbutyral) compositions used herein preferably incorporate 0 to about 10.0wt %, or more preferably, 0 to about 5.0 wt %, or most preferably, 0 toabout 1.0 wt %, of thermal stabilizers, based on the total weight of thecomposition.

The poly(vinyl butyral) used herein may further contain an effectiveamount of UV absorbers. UV absorbers are well-know in the art. Any knownUV absorber may find utility within the present invention. Preferablegeneral classes of UV absorbers include, but are not limited to,benzotriazoles, hydroxybenzophenones, hydroxyphenyl triazines, esters ofsubstituted and unsubstituted benzoic acids, and the like and mixturesthereof. The compositions used herein may include 0 to about 10.0 wt %,or preferably, 0 to about 5.0 wt %, or more preferably, 0 to about 1.0wt %, of UV absorbers, based on the total weight of the composition.

The poly(vinyl butyral) compositions used herein may also incorporate aneffective amount of hindered amine light stabilizers (HALS). Hinderedamine light stabilizers are well-know in the art. Generally, HALS aredisclosed to be secondary, tertiary, acetylated, N-hydrocarbyloxysubstituted, hydroxy substituted N-hydrocarbyloxy substituted, or othersubstituted cyclic amines which further incorporate steric hindrance,generally derived from aliphatic substitution on the carbon atomsadjacent to the amine function. The compositions used herein may contain0 to about 10.0 wt %, or preferably, 0 to about 5.0 wt %, or 0 to about1.0 wt %, of HALS, based on the total weight of the composition.

The poly(vinyl butyral) sheets used herein may be produced through anyknown process. Generally, the poly(vinyl butyral) sheets are producedthrough extrusion casting processes. The sheets may have smooth orroughened surfaces. Preferably, the poly(vinyl butyral) sheets usedherein have roughened surfaces to facilitate de-airing during thelamination process.

Plasticized poly(vinyl butyral) sheets used herein may be formed byinitially mixing the poly(vinyl butyral) resin composition withplasticizer and then extruding the formulation through a sheet-shapingdie, i.e. forcing molten, plasticized poly(vinyl butyral) through ahorizontally long, vertically narrow die opening substantiallyconforming in length and width to that of the sheet being formed. Theplasticized poly(vinyl butyral) compositions can generally be extrudedat a temperature of from about 225° C. to about 245° C. Rough surfaceson one or both sides of the extruding sheet are preferably provided bythe design of the die opening and the temperature of the die exitsurfaces through which the extrudate passes, as disclosed in, e.g., U.S.Pat. No. 4,281,980. Alternative techniques for producing a preferablerough surface on an extruding poly(vinyl butyral) sheet involve thespecification and control of one or more of polymer molecular weightdistribution, water content and melt temperature. The sheet formation ofpoly(vinyl butyral) is disclosed in U.S. Pat. Nos. 2,904,844; 2,909,810;3,679,788; 3,994,654; 4,161,565; 4,230,771; 4,292,372; 4,297,262;4,575,540; 5,151,234; 5,886,675 and European Patent No. EP 0 185 863.Alternatively, the sheet in the “as extruded” condition may be passedover a specially prepared surface of a die roll positioned in closeproximity to the exit of the die which imparts the preferable surfacecharacteristics to one side of the molten polymer. Thus, when thesurface of such roll has minute peaks and valleys, sheet formed ofpolymer cast thereon will have a rough surface on the side whichcontacts the roll which generally conforms respectively to the valleysand peaks of the roll surface. Such die rolls are disclosed in, e.g.,U.S. Pat. No. 4,035,549. A roughened sheet surface is preferred tosimplify the lamination process and to provide superior solar celllaminates. It is understood that such rough surface is only temporaryand particularly functions to facilitate de-airing during laminating andafter which it is melted smooth from the elevated temperature andpressure associated with autoclaving and other lamination processes.

The thickness of the poly(vinyl butyral) sheet used herein may be anythickness desired for the solar cell laminate structure. Preferably, thepoly(vinyl butyral) sheet has a thickness less than or equal to about 30mils (0.76 mm), or more preferably, less than or equal to about 20 mils(0.51 mm), or most preferably, from about 10 mils (0.25 mm) to about 20mils.

II. Film Layers

Besides the first sub-layer of a poly(vinyl butyral) sheet, thepreformed bi-layer sheet disclosed herein further comprises a secondsub-layer of a metal film, such as aluminum foil, or a polymeric film.Polymers suitable for the polymeric films include, but are not limitedto, poly(ethylene terephthalate) (PET), polycarbonate, polypropylene,polyethylene, polypropylene, cyclic polyolefins, norbornene polymers,polystyrene, syndiotactic polystyrene, styrene-acrylate copolymers,acrylonitrile-styrene copolymers, poly(ethylene naphthalate),polyethersulfone, polysulfone, nylons, poly(urethanes), acrylics,cellulose acetates, cellulose triacetates, cellophane, vinyl chloridepolymers, polyvinylidene chloride, vinylidene chloride copolymers,fluoropolymers, polyvinyl fluoride, polyvinylidene fluoride,polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymers and thelike. Preferably, the film is selected from the group consisting ofbi-axially oriented PET films, coated bi-axially oriented PET films, andfluoropolymer films, e.g., poly(vinyl fluoride) or poly(vinylidenefluoride) films, such as Tedlar® or Tefzel® films, which are commercialproducts of DuPont. More preferably, the film is selected from the groupconsisting of bi-axially oriented PET films and coated bi-axiallyoriented PET films.

In accordance to the present invention, one or both surfaces of the filmlayers may be treated to enhance the adhesion to the other laminatelayers in the solar cell laminates. This treatment may take any formknown within the art, including adhesives, primers, such as silanes,flame treatments, such as those disclosed within U.S. Pat. Nos.2,632,921; 2,648,097; 2,683,894 and 2,704,382, plasma treatments, suchas those disclosed within U.S. Pat. No. 4,732,814, electron beamtreatments, oxidation treatments, corona discharge treatments, chemicaltreatments, chromic acid treatments, hot air treatments, ozonetreatments, ultraviolet light treatments, sand blast treatments, solventtreatments, and the like and combinations thereof. For example, a thinlayer of carbon may be deposited on one or both surfaces of thepolymeric film through vacuum sputtering as disclosed in U.S. Pat. No.4,865,711. For example, U.S. Pat. No. 5,415,942 discloses ahydroxy-acrylic hydrosol primer coating that may serve as anadhesion-promoting primer for PET films.

Preferably, the adhesive or primer is a silane which incorporates anamine function. Specific examples of such materials include, but are notlimited to, gamma-aminopropyltriethoxysilane,N-beta-(aminoethyl)-gamma-aminopropyl-trimethoxysilane, and the like andmixtures thereof. Commercial examples of such materials include, e.g.,A-1100® silane (from the Silquest Company, formerly from the UnionCarbide Company, believed to be gamma-aminopropyltrimethoxysilane) andZ6020® silane (from the Dow Company).

More preferably, the polymeric film used herein includes a primercoating on one or both surfaces, more preferably both surfaces,comprising a coating of a polyallylamine-based primer. Thepolyallylamine-based primer and its application to a PET film isdisclosed within U.S. Pat. Nos. 5,411,845; 5,770,312; 5,690,994; and5,698,329. Generally, PET film is extruded and cast as a film byconventional methods, as described above, and the polyallylamine coatingis applied to the PET film either before stretching or between themachine direction stretching and transverse direction stretchingoperations, and/or after the two stretching operations and heat settingin the tenter oven. It is preferable that the coating be applied beforethe transverse stretching operation so that the coated PET web is heatedunder restraint to a temperature of about 220° C. in the tenter oven inorder to cure the polyallylamine to the PET film surface(s). Suchmaterials are disclosed within, e.g.; U.S. Patent Application No.2005/0129954. In addition to this cured coating, an additionalpolyallylamine coating can be applied on it after the stretching andtenter oven heat setting in order to obtain a thicker overall coating.

The thickness of the film layer used here in the preformed bi-layersheet is not critical and may be varied depending on the particularapplication. Generally, the thickness of the film layer may range fromabout 0.1 mils (0.003 mm) to about 10 mils (0.26 mm), more preferably,from about 1 mil to about 7 mils (0.18 mm).

The polymeric film used herein is preferably sufficientlystress-relieved and shrink-stable under the coating and laminationprocesses. Preferably, the polymeric film used herein is heat stabilizedto provide low shrinkage characteristics when subjected to elevatedtemperatures (i.e. less than 2% shrinkage in both directions after 30minutes at 150° C.), such are seen through the lamination processesdescribed below.

The film layer of the preformed bi-layer sheet disclosed herein may becoated if desired. For example, the coating may function as oxygen andmoisture barrier coatings, such as the metal oxide coating disclosedwithin, e.g., U.S. Pat. Nos. 6,521,825 and 6,818,819 and European PatentNo. EP 1 182 710.

The film layer used herein may also have a hard coat layer on one orboth surfaces. It is particularly preferable that any film surface havea hard coat if it is to be utilized as an outside laminate surface. Anyhard coat formulation known within the art may be utilized. Generally,the hard coat layers are formed from an UV curing resin. Any resin thatis UV curable may be usable. Specific examples of materials for the UVcuring resin include, e.g., oligomers, such as urethane oligomers,polyester oligomers, and epoxy oligomers that have two or moreethylenically double bonds, mono- or poly-functional oligomers, such as,e.g., pentaerythritol tetraacrylate (PETA), pentaerythritoltetramethacrylate, and dipentaerythritol hexaacrylate (DPEHA), and thelike and mixtures thereof. The UV curing resin generally consists of anoligomer, a photoinitiator, and, if desired, a reactive diluent(monomer). Specific examples of the photoinitiator includes, e.g.,benzoin, benzophenone, benzoyl methyl ether, benzoin ethyl ether,benzoin isopropyl ether, benzoin isobutyl ether, dibenzyl,5-nitroacenaphtene, hexachlorocyclopentadiene, p-nitrodiphenyl,p-nitroaniline, 2,4,6-trinitroaniline, 1,2-benzanthraquinone,3-methyl-1,3-diaza-1,9-benzanthrone, and the like and mixtures thereof.The level of the diluent is preferably within the range from about 0.1to about 10 wt %, or more preferably, from about 0.5 to about 5 wt %,based on the total weight of the UV curable resin. The level of thephotoinitiator is preferably less than or equal to about 5 wt % based onthe total weight of the UV curable resin. The hard coat may be appliedto the film through typical solution coating processes.

The hard coat may also incorporate further additives or be modified toprovide other desirable attributes, such as a high scratch-resistance.Generally, to enhance the scratch resistance of the hard coat layer, thepencil hardness must be increased. Preferably, the scratch-resistanthard coat layer should have a pencil hardness of 5H or greater, or morepreferably, 8H or greater, or most preferably, 9H or greater. The hardcoat may contain fine particles of SiO₂, TiO₂, ZrO₂, Al₂O₃ or MgO toimprove the hardness and wear resistance. These particles are basicallytransparent and do not lower the transmittance of visible light by afilm. An example of a scratch-resistant hard coat layer additiveincludes UVCH1105® resin that is commercially available from the ToshibaSilicone Corporation. Abrasion resistant polysiloxane and oligomerichardcoat materials are disclosed in U.S. Patent Application No.20050077002. Further examples of abrasion resistant useful hereininclude silica and organic silanol coatings that are disclosed withinU.S. Pat. No. 4,177,315.

The hard coat layer may further incorporate fog-resistant additives toprevent dew condensation and the loss of film transparency thereby. Thisis especially important when a surface of the film forms an outsidelayer of the solar cell laminates of the present invention. Generally,to provide fog-resistance, hydrophilic oligomers and monomers orsurfactants (especially wetting agents) are utilized. The fog-resistanthard coat layer may be formed using, e.g., DIABEAM® MH-3263 resinavailable from the Mitsubishi Rayon Co., Ltd.

The hard coat layer may further incorporate additives which provide highgloss, preferably a glass level of at least 95 (according to JIS K 7105)or greater. An example of the high gloss hard coat layer can be formedusing, e.g., ADEKA OPTMER® KR-567 available from the ASAHI DENKA KOGYOK.K. Company.

The hard coat layer may further incorporate additives which provide highsolvent resistance, especially excellent solvent resistance to highlypolar solvents, such as N,N′-dimethylformamide. Generally, such solventresistant hard coat compositions will include a hydrophobic additive,such as, e.g., a silicon- or fluorine-modified oligomers, monomers orresin. An example of a solvent resistant hard coat composition is, e.g.,Silicone Hard Coat Agent® KP851 resin available from the Shin-EtsuChemical Co., Ltd.

The hard coat layer may further incorporate additives which increase themoisture barrier properties of the film. Generally, such moisturebarrier hard coat compositions may include a hydrophobic additive, suchas, e.g., a silicon- or fluorine-modified oligomers, monomers or resin.An example of a moisture barrier hard coat composition is, e.g.,Ultraviolet Curing Resin Having Low Permeability available from NIPPONKASEI Co., Ltd.

The films may further have modified surfaces. For example, the films mayhave coatings of antistatic materials. Examples of the antistatic agentinclude ionic polymer compounds, surfactants, conductive inorganic fineparticles, inorganic electrolytes, organic complex salts, and the like.The term “ionic polymer compounds” is a general term for polymercompounds each having an ionic group in a main chain or side chain, oras a pendant of the main chain. Examples of ionic groups of polymercompounds each having an ionic group include, but are not limited to,anionic groups of sulfonates, carboxylates, phosphates, alkylsulfonatesalts, alkylphosphate salts, and the like; cationic groups of compoundseach mainly composed of a tertiary ammonium salt such as analkyltrimethylammonium salt, lauryltrimethylammonium chloride, analkylpyrrolidium salt, or the like; nonionic groups of compounds eachmainly composed of a polyether, a polyhydric alcohol, a polyoxyethylenealkylamine, a polyoxyethylene fatty acid ester, or the like; long chainfatty acid groups; ampholyte ions of compounds each having tertiaryammonium nitrogen and a carboxyl group or sulfone group; and the like.Examples of a polymer compound having an ionic group in a main chaininclude polymer compounds each having a pyrrolidium ring, a piperidiumring, or the like in its main chain; and these polymer compounds eachfurther containing, as a comonomer, a compound having an unsaturatedbond. Examples of a polymer compound having an ionic group in its sidechain include polymer compounds each having a main chain comprising ahomopolymer of acrylic acid, methacrylic acid, styrene, or the likeand/or a copolymer with another component such as a saturatedhydrocarbon such as ethylene, propylene, or the like, an unsaturatedhydrocarbon such as acetylene, or the like, or alkyleneoxide, and a sidechain having an ionic group of a phosphate salt, a sulfonate salt, avinylsulfonate salt, a carboxylate salt, a tertiary ammonium salt, orthe like.

III. Preparation of the Preformed Bi-Layer Sheets

The processes to pre-form the bi-layer sheets disclosed herein may takemany forms and may be produced through any known method. For example,the preformed bi-layer sheets may be produced through co-extrusion,whereby two or more slit dies are utilized, or by extrusion coating, forexample, of the poly(vinyl butyral) sub-layer onto a preformed filmlayer.

Preferably, the preformed bi-layer sheets disclosed herein are producedthrough lamination of preformed poly(vinyl butyral) sheets withpreformed film layers. For example, the poly(vinyl butyral) sheet may belightly bonded to the film layer through a nip roll bonding process. Insuch a process, the film is supplied from a roll and first passes over atension roll. The film may be subjected to moderate heating by passingthrough a heating zone, such as an oven. The poly(vinyl butyral) sheetmay also be supplied from a roll or as flat sheet stock and first passesover a tension roll. The poly(vinyl butyral) sheet may be subjected tomoderate heating by passing through a heating zone, such as an oven.Heating should be to a temperature sufficient to promote temporaryfusion bonding, i.e., to cause the surfaces of the poly(vinyl butyral)sheet to become tacky. Suitable temperatures for a preferred poly(vinylbutyral) sheet is within the range of about 50° C. to about 120° C.,with the preferred surface temperatures reaching about 65° C.

The film layer may be fed along with the poly(vinyl butyral) sheetthrough nip rolls where the two layers are merged together undermoderate pressure to form a weakly bonded laminate. If desired, the niprolls may be heated to promote the bonding process. The bonding pressureexerted by the nip rolls may vary with the film materials, thepoly(vinyl butyral) materials and the temperatures employed. Generallythe bonding pressure may be within the range of about 10 psi (0.7kg/cm²) to about 75 psi (5.3 kg/cm²), or preferably, about 25 psi (1.8kg/cm²) to about 30 psi (2.1 kg/cm²). The tension between the poly(vinylbutyral) sheet and the film layer is controlled by passage over an idlerroll. Typical line speeds through the roll assembly are within the rangeof about 5 feet (1.5 m) to about 30 feet (9.2 m), per minute. Propercontrol of the speed and the tension tends to minimize wrinkling of thefilm. After bonding, the preformed bi-layer sheet is passed over aseries of cooling rolls which ensure that the sheet taken up on a rollis not tacky. Water cooling is generally sufficient to achieve thisobjective. Tension within the system may be further maintained throughthe use of idler rolls. Sheets made through this process will havesufficient strength to allow handling by laminators who will produce thefinal solar cell laminates which incorporate these preformed bi-layersheets.

Such preformed poly(vinyl butyral)/film bi-layer composite sheets arealso commercially available under the trade name SentryGlas® SpallShieldby DuPont. For example, SentryGlas® Spallshield 3010 is a bi-layercomposite consisting of a 30 mil (0.76 mm) thick poly(vinyl butyral)sheet and a 10 mil (0.25 mm) thick polyester film layer; SentryGlas®Spallshield 1510 is a bi-layer composite consisting of a 15 mil (0.38mm) thick poly(vinyl butyral) sheet and a 10 mil (0.25 mm) thickpolyester film layer; and SentryGlas® Spallshield 307 is a bi-layercomposite consisting of a 30 mil (0.76 mm) thick poly(vinyl butyral)sheet and a 7 mil (0.18 mm) thick polyester film layer.

Solar Cell Modules or Laminates

Solar cells are commonly available on an ever increasing variety as thetechnology evolves and is optimized. Within the present invention, asolar cell is meant to include any article which can convert light intoelectrical energy. Typical art examples of the various forms of solarcells include, for example, single crystal silicon solar cells,polycrystal silicon solar cells, microcrystal silicon solar cells,amorphous silicon based solar cells, copper indium selenide solar cells,compound semiconductor solar cells, dye sensitized solar cells, and thelike. The most common types of solar cells include multi-crystallinesolar cells, thin film solar cells, compound semiconductor solar cellsand amorphous silicon solar cells due to relatively low costmanufacturing ease for large scale solar cells.

Thin film solar cells are typically produced by depositing several thinfilm layers onto a substrate, such as glass or a flexible film, with thelayers being patterned so as to form a plurality of individual cellswhich are electrically interconnected to produce a suitable voltageoutput. Depending on the sequence in which the multi-layer deposition iscarried out, the substrate may serve as the rear surface or as a frontwindow for the solar cell module. By way of example, thin film solarcells are disclosed in U.S. Pat. Nos. 5,512,107; 5,948,176; 5,994,163;6,040,521; 6,137,048; and 6,258,620. Examples of thin film solar cellmodules are those that comprise cadmium telluride or CIGS,(Cu(In—Ga)(SeS)2), thin film cells.

Now referring to FIG. 2, a typical prior art solar cell laminate ormodule 20 consists of (i) a solar cell layer 23 that is formed of one ora plurality of electronically interconnected solar cells, (ii) one ormore encapsulant layers laminated to either side of the solar celllayer, such as the front-sheet encapsulant layer 22 that is laminated tothe light-receiving side 23 a of the solar cell layer and the back-sheetencapsulant layer 24 that is laminated to the back side 23 b of thesolar cell layer, (iii) a first outer layer on the light-receiving sideof the laminate, i.e., the incident layer 21; (iv) a second outer layeron the rear side of the laminate, i.e., the back-sheet 25; and (v)optionally other functional film or sheet layers embedded with thelaminate, such as dielectric layers or barrier layer (e.g., moisture oroxygen barrier layers). It is essential that all the film or sheetlayers laminated to the light-receiving side of the solar cell layer aremade of transparent materials to allow efficient transmission ofsunlight into the solar cell(s). In some instances, a special film orsheet layer may be included to serve both the function of an encapsulantlayer and an outer layer, e.g., an incident layer or a back-sheet. It isalso conceivable that any of the film or sheet layers included in thelaminates may be formed of single- or multi-layer films or sheets.

In general, the encapsulant layer(s) of a solar cell laminate may bederived from any type of suitable films or sheets. Such suitable filmsor sheets include, but are not limited to, films or sheets comprisingpoly(vinyl butyral), ionomers, EVA, acoustic poly(vinyl acetal),acoustic poly(vinyl butyral), PU, PVC, metallocene-catalyzed linear lowdensity polyethylenes, polyolefin block elastomers, ethylene acrylateester copolymers, such as poly(ethylene-co-methyl acrylate) andpoly(ethylene-co-butyl acrylate), acid copolymers, silicone elastomersand epoxy resins. The encapsulant layer(s) comprised in the solar celllaminates may have smooth or roughened surfaces. Preferably, theencapsulant layer(s) have roughened surfaces to facilitate the de-airingof the laminates through the laminate process.

The outer layers of the solar cell laminates, i.e., the incident layersand the back-sheets, may be derived from any suitable sheets or films.Suitable sheets used herein may be glass or plastic sheets, such as,polycarbonate, acrylics, polyacrylate, cyclic polyolefins, such asethylene norbornene polymers, metallocene-catalyzed polystyrene,polyamides, polyesters, fluoropolymers and the like and combinationsthereof, or metal sheets, such as aluminum, steel, galvanized steel, andceramic plates.

Glass may serve as the incident layer of the solar cell laminate and thesupportive back-sheet of the solar cell module may be derived fromglass, rigid plastic sheets or metal sheets. The term “glass” is meantto include not only window glass, plate glass, silicate glass, sheetglass, low iron glass, tempered glass, tempered CeO-free glass, andfloat glass, but also includes colored glass, specialty glass whichincludes ingredients to control, for example, solar heating, coatedglass with, for example, sputtered metals, such as silver or indium tinoxide, for solar control purposes, E-glass, Toroglass, Solex® glass (aproduct of Solutia) and the like. Such specialty glasses are disclosedin, for example, U.S. Pat. Nos. 4,615,989; 5,173,212; 5,264,286;6,150,028; 6,340,646; 6,461,736; and 6,468,934. The type of glass to beselected for a particular laminate depends on the intended use.

The film layers used herein may be metal or polymeric. The specifics ofthese film layers are similar to those films used in the preformedbi-layer sheets, as described above.

The films used herein may serve as an incident layer (such as thefluoropolymer or PET film) or a back-sheet (such as the fluoropolymer,aluminum foil, or PET film).

The optional other functional film or sheet layers embedded with thelaminate, such as the dielectric layers or barrier layers, may bederived from any of the above mentioned polymeric films that are coatedwith additional functional coatings. For example, PET films coated witha metal oxide coating, such as those disclosed within U.S. Pat. Nos.6,521,825 and 6,818,819 and European Patent No. EP 1 182 710, mayfunction as oxygen and moisture barrier layers in the laminates.

If desired, a layer of non-woven glass fiber (scrim) may also beincluded in the solar cell laminates to facilitate de-airing during thelamination process or to serve as reinforcement for the encapsulantlayer(s). The use of such scrim layers within solar cell laminates isdisclosed within, for example, U.S. Pat. Nos. 5,583,057; 6,075,202;6,204,443; 6,320,115; 6,323,416; and European Patent No. 0 769 818.

In accordance to the present invention, however, the solar cell laminateof the present invention comprises at least one layer of the preformedbi-layer sheet 10 (as shown in FIG. 1) serving as an encapsulant layer.

In one aspect, the solar cell laminate of the present inventioncomprises at least one layer of the preformed bi-layer sheet 10 whichhas the poly(vinyl butyral) sub-layer 12 in a closer proximity to thesolar cell layer.

In one particular embodiment (as shown in FIG. 3), the preformedbi-layer sheet 10 is included in solar cell laminate 20 a as afront-sheet encapsulant layer 22 having the poly(vinyl butyral)sub-layer 12 in direct contact with and adhered to solar cell layer 23at the light-receiving side 23 a. The solar cell laminate 20 a mayfurther comprise at least one back-sheet encapsulant layer 24 and a backsheet 25. In this particular embodiment, the preformed bi-layer sheet 10may function as both a front-sheet encapsulant layer 22 and an incidentlayer 21. Or, as shown in FIG. 4, besides the preformed bi-layer sheet10, the solar cell layer 23, the back-sheet encapsulant layer 24, andthe back-sheet 25, solar cell laminate 20 b further comprises anincident layer 21 and at least one additional front-sheet encapsulantlayer 22 a. In this particular embodiment, the preformed bi-layer sheet10 serves as a front-sheet encapsulant layer and due to the lack ofadhesion between the film sub-layer 14 and the incident layer 21, the atleast one additional front-sheet encapsulant layer 22 a is incorporatedbetween the preformed bi-layer sheet 10 and the incident layer 21 toform a bond between the two layers.

In another particular embodiment (as shown in FIG. 5), the preformedbi-layer sheet 10 is included in solar cell laminate 20 c as aback-sheet encapsulant layer 24 having the poly(vinyl butyral) sub-layer12 in direct contact with and adhered to solar cell layer 23 at the backside 23 b. The solar cell laminate 20 c may further comprise afront-sheet encapsulant layer 22 and an incident layer 21. In thisparticular embodiment, the preformed bi-layer sheet 10 may function asboth a back-sheet encapsulant layer 24 and a back-sheet 25. Or, as shownin FIG. 6, besides the incident layer 21, the at least one front-sheetencapsulant layer 22, the solar cell layer 23, the preformed bi-layersheet 10, solar cell laminate 20 d may further comprise a back-sheet 25and at least one additional back-sheet encapsulant layer 24 a. In thisparticular embodiment, the preformed bi-layer sheet 10 serves as aback-sheet encapsulant layer 24 and due to the lack of adhesion betweenthe film sub-layer 14 and the back-sheet 25, the at least one additionalback-sheet encapsulant layer 24 a is incorporated between the preformedbi-layer sheet 10 and the back-sheet 25 to form a bond between the twolayers.

In yet another particular embodiment (as shown in FIG. 7), solar celllaminate 20 e may comprise two (2) layers of the preformed bi-layersheet 10. In this particular embodiment, the two preformed bi-layersheets 10 are laminated to each side of solar cell layer 23 with theirpoly(vinyl butyral) sub-layers in a closer proximity to the solar cell23. Optionally, an incident layer and/or a back-sheet layer and/oradditional encapsulant layer(s) may also be included in solar celllaminate 20 e.

In another aspect, the solar cell laminate of the present inventioncomprises at least one layer of the preformed bi-layer sheet 10 whichhas the film sub-layer 14 in a closer proximity to the solar cell layer.In such cases, due to the lack of adhesion between the film sub-layer 14and the solar cell layer, at least one additional encapsulant layer isplaced between the preformed bi-layer sheet 10 and the solar cell layer23 to form a bond between the two.

In one particular embodiment, as shown in FIG. 8, the at least onepreformed bi-layer sheet 10 is included in solar cell laminate 20 f as afront-sheet encapsulant layers 22 with its film sub-layer 14 in a closerproximity to solar cell layer 23 at the light-receiving side 23 a. Inaddition, an additional front-sheet encapsulant layer 22 a is placedbetween the preformed bi-layer sheet 10 and the solar cell layer 23 toform a bond between the two. In this particular embodiment, solar celllaminate 20 f may further comprise an incident layer 21 laminated to thepoly(vinyl butyral) sub-layer 12 of the preformed bi-layer sheet 10, aback-sheet encapsulant layer 24, and a back-sheet 25.

In another embodiment, as shown in FIG. 9, the at least one preformedbi-layer sheet 10 is included in solar cell laminate 20 g as aback-sheet encapsulant layer 24 with its film sub-layer 14 in a closerproximity to solar cell layer 23 at the back side 23 b. In addition, anadditional back-sheet encapsulant layer 24 a is placed between thepreformed bi-layer sheet 10 and the solar cell layer 23 to form a bondbetween the two. In this particular embodiment, solar cell laminate 20 gmay further comprise a back-sheet 25 laminated to the poly(vinylbutyral) sub-layer 12 of the preformed bi-layer sheet 10, a front-sheetencapsulant layer 22, and an incident layer 21.

It is understood that these particular embodiments described above orillustrated in the figures may further comprise other additional layersof sheets or films. In addition, the scope of the present inventionshould not be limited to these particular embodiments. Basically, anysolar cell laminate or module comprising at least one layer of thepreformed bi-layer sheet 10, as disclosed herein, is within the scope ofthe present invention.

Also in accordance to the present invention, if greater adhesion isdesired, one or both surfaces of any of the composite layers of thesolar cell laminate of the present invention may be treated to enhancethe adhesion to other laminate layers. This treatment may take any formknown within the art, including adhesives, primers, such as silanes,flame treatments, such as disclosed within U.S. Pat. Nos. 2,632,921;2,648,097; 2,683,894; and 2,704,382, plasma treatments, such asdisclosed within U.S. Pat. No. 4,732,814, electron beam treatments,oxidation treatments, corona discharge treatments, chemical treatments,chromic acid treatments, hot air treatments, ozone treatments,ultraviolet light treatments, sand blast treatments, solvent treatments,and the like and combinations thereof. For example, a thin layer ofcarbon may be deposited on one or both surfaces of the polymeric filmthrough vacuum sputtering as disclosed in U.S. Pat. No. 4,865,711. Or,as disclosed in U.S. Pat. No. 5,415,942, a hydroxy-acrylic hydrosolprimer coating that may serve as an adhesion-promoting primer forpoly(ethylene terephthalate) films.

In a particular embodiment, the adhesive layer may take the form of acoating. The thickness of the adhesive/primer coating may be less than 1mil, or preferably, less than 0.5 mil, or more preferably, less than 0.1mil. The adhesive may be any adhesive or primer known within the art.Specific examples of adhesives and primers which may be useful in thepresent invention include, but are not limited to,gamma-chloropropylmethoxysilane, vinyltrichlorosilane,vinyltriethoxysilane, vinyltris(beta-methoxyethoxy)silane,gamma-methacryloxypropyltrimethoxysilane,beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,gammaglycidoxypropyltrimethoxysilane, vinyl-triacetoxysilane,gamma-mercaptopropyltrimethoxysilane, gamma-aminopropyltriethoxysilane,N-beta-(aminoethyl)-gamma-aminopropyl-trimethoxysilane, glue, gelatine,caesin, starch, cellulose esters, aliphatic polyesters,poly(alkanoates), aliphatic-aromatic polyesters, sulfonatedaliphatic-aromatic polyesters, polyamide esters, rosin/polycaprolactonetriblock copolymers, rosin/poly(ethylene adipate) triblock copolymers,rosin/poly(ethylene succinate) triblock copolymers, poly(vinylacetates), poly(ethylene-co-vinyl acetate), poly(ethylene-co-ethylacrylate), poly(ethylene-co-methyl acrylate),poly(ethylene-co-propylene), poly(ethylene-co-1-butene),poly(ethylene-co-1-pentene), poly(styrene), acrylics, polyurethanes,sulfonated polyester urethane dispersions, nonsulfonated urethanedispersions, urethane-styrene polymer dispersions, non-ionic polyesterurethane dispersions, acrylic dispersions, silanated anionicacrylate-styrene polymer dispersions, anionic acrylate-styrenedispersions, anionic acrylate-styrene-acrylonitrile dispersions,acrylate-acrylonitrile dispersions, vinyl chloride-ethylene emulsions,vinylpyrrolidone/styrene copolymer emulsions, carboxylated andnoncarboxylated vinyl acetate ethylene dispersions, vinyl acetatehomopolymer dispersions, polyvinyl chloride emulsions, polyvinylidenefluoride dispersions, ethylene acrylic acid dispersions, polyamidedispersions, anionic carboxylated or noncarboxylatedacrylonitrile-butadiene-styrene emulsions and acrylonitrile emulsions,resin dispersions derived from styrene, resin dispersions derived fromaliphatic and/or aromatic hydrocarbons, styrene-maleic anhydrides, andthe like and mixtures thereof.

In another particular embodiment, the adhesive or primer is a silanethat incorporates an amine function. Specific examples of such materialsinclude, but are not limited to, gamma-aminopropyltriethoxysilane,N-beta-(aminoethyl)-gamma-aminopropyl-trimethoxysilane, and the like andmixtures thereof. Commercial examples of such materials include, forexample A-1100® silane, (from the Silquest Company, formerly from theUnion Carbide Company, believed to be gamma-aminopropyltrimethoxysilane)and Z6020® silane, (from the Dow Corning Corp.).

The adhesives may be applied through melt processes or through solution,emulsion, dispersion, and the like, coating processes. One of ordinaryskill in the art will be able to identify appropriate process parametersbased on the composition and process used for the coating formation. Theabove process conditions and parameters for making coatings by anymethod in the art are easily determined by a skilled artisan for anygiven composition and desired application. For example, the adhesive orprimer composition can be cast, sprayed, air knifed, brushed, rolled,poured or printed or the like onto the surface. Generally the adhesiveor primer is diluted into a liquid medium prior to application toprovide uniform coverage over the surface. The liquid media may functionas a solvent for the adhesive or primer to form solutions or mayfunction as a non-solvent for the adhesive or primer to form dispersionsor emulsions. Adhesive coatings may also be applied by spraying themolten, atomized adhesive or primer composition onto the surface. Suchprocesses are disclosed within the art for wax coatings in, for example,U.S. Pat. Nos. 5,078,313; 5,281,446; and 5,456,754.

Notably, specific solar cell laminate constructions (top (lightincident) side to back side) include, but are not limited to,[film/PVB]/solar cell/[PVB/film]; glass/other encapsulant layer/solarcell/[PVB/film]; Tedlar® film/other encapsulant layer/solarcell/[PVB/film]; [film/PVB]/solar cell/other encapsulant layer/glass;[film/PVB]/solar cell/other encapsulant layer/Tedlar® film;[film/PVB]/solar cell/other encapsulant layer/PET film; [film/PVB]/solarcell/other encapsulant layer/aluminum stock; [film/PVB]/solar cell/otherencapsulant layer/galvanized steel sheet; [film/PVB]/[film/PVB]/solarcell/[PVB/film]; [film/PVB]/[film/PVB]/solar cell/[PVB/film]/[PVB/film];glass/other encapsulant layer/solar cell/[PVB/film]/[PVB/film];glass/[PVB/film]/other encapsulant layer/solar cell/[PVB/film];glass/other encapsulant layer/[film/PVB]/solar cell/[PVB/film];[film/PVB]/solar cell/[PVB/film]/other encapsulant layer/aluminum stock;[film/PVB]/solar cell/other encapsulant layer/[film/PVB]/aluminum stock;[film/PVB]/solar cell/[PVB/film]/other encapsulant layer/galvanizedsteel sheet; [film/PVB]/solar cell/other encapsulantlayer/[film/PVB]/galvanized steel sheet; glass/other encapsulantlayer/solar cell/[PVB/film]/other encapsulant layer/aluminum stock;glass/other encapsulant layer/solar cell/other encapsulantlayer/[film/PVB]/aluminum stock; glass/other encapsulant layer/solarcell/[PVB/film]/other encapsulant layer/galvanized steel sheet;glass/other encapsulant layer/solar cell/other encapsulantlayer/[film/PVB]/galvanized steel sheet, wherein “film/PVB” or“PVB/film” are used herein to denote the preformed bi-layer sheet 10.

The use of the poly(vinyl butyral) containing preformed bi-layer sheetsin solar cell laminates has been proven to be more beneficial than usinga poly(vinyl butyral) sheet directly in solar cell laminates. First, thefilm sub-layer of the preformed bi-layer sheet helps to reduce oreliminate the tendency of the poly(vinyl butyral) sheet to block orstick together within the roll during storage or shipment under ambientconditions. This is accomplished by not allowing the poly(vinyl butyral)surfaces to come in contact with each other, and, in turn, to stick orblock together. In addition, due to the reduction or elimination of thelayer blocking tendency, the two step lamination process that isrequired when laminating a poly(vinyl butyral) sheet directly to otherfilms or sheets has become unnecessary and thereby greatly simplifyingthe lamination process. Moreover, as discussed above, during theconventional process, when poly(vinyl butyral) sheets are used aslaminate layers, interleave layers, e.g., PET film layers, are oftenused during the lamination process and then discarded as undesirablewaste. In the present invention, however, the film sub-layer of thepreformed bi-layer sheet serves as an interleave layer to the poly(vinylbutyral) sheet, and, instead of being discarded, the film sub-layerremains in the laminate providing additional function(s).

Manufacture of Solar Cell Module or Laminate

In a further embodiment, the present invention is a simplified processof manufacturing a solar cell laminate comprising a preformed poly(vinylbutyral) containing bi-layer sheet disclosed herein.

Specifically, unlike those solar cell laminates containing poly(vinylbutyral) sheets, the preformed bi-layer sheets disclosed herein can besimply laid up with other laminate layers and subject to furtherlamination process, as described below.

The solar cell laminates of the present invention may be producedthrough autoclave and non-autoclave processes, as described below. Forexample, the solar cell constructs described above may be laid up in avacuum lamination press and laminated together under vacuum with heatand standard atmospheric or elevated pressure.

In an exemplary process, a glass sheet, a front-sheet encapsulant layer,a solar cell, a back-sheet encapsulant layer and Tedlar® film, and acover glass sheet are laminated together under heat and pressure and avacuum (for example, in the range of about 27-28 inches (689-711 mm) Hg)to remove air. Preferably, the glass sheet has been washed and dried. Atypical glass type is 90 mil thick annealed low iron glass. In anexemplary procedure, the laminate assembly of the present invention isplaced into a bag capable of sustaining a vacuum (“a vacuum bag”),drawing the air out of the bag using a vacuum line or other means ofpulling a vacuum on the bag, sealing the bag while maintaining thevacuum, placing the sealed bag in an autoclave at a temperature of about120° C. to about 180° C., at a pressure of about 200 psi (about 15bars), for from about 10 to about 50 minutes. Preferably the bag isautoclaved at a temperature of from about 120° C. to about 160° C. for20 minutes to about 45 minutes. More preferably the bag is autoclaved ata temperature of from about 135° C. to about 160° C. for about 20minutes to about 40 minutes. A vacuum ring may be substituted for thevacuum bag. One type of vacuum bag is disclosed within U.S. Pat. No.3,311,517.

Any air trapped within the laminate assembly may be removed through anip roll process. For example, the laminate assembly may be heated in anoven at a temperature of about 80° C. to about 120° C., or preferably,at a temperature of between about 90° C. and about 100° C., for about 30minutes. Thereafter, the heated laminate assembly is passed through aset of nip rolls so that the air in the void spaces between the solarcell outside layers, the solar cell and the encapsulant layers may besqueezed out, and the edge of the assembly sealed. This process mayprovide the final solar cell laminate or may provide what is referred toas a pre-press assembly, depending on the materials of construction andthe exact conditions utilized.

The pre-press assembly may then be placed in an air autoclave where thetemperature is raised to about 120° C. to about 160° C., or preferably,between about 135° C. and about 160° C., and pressure to between about100 psig and about 300 psig, or preferably, about 200 psig (14.3 bar).These conditions are maintained for about 15 minutes to about 1 hour, orpreferably, about 20 to about 50 minutes, after which, the air is cooledwhile no more air is added to the autoclave. After about 20 minutes ofcooling, the excess air pressure is vented and the solar cell laminatesare removed from the autoclave. This should not be considered limiting.Essentially any lamination process known within the art may be used withthe encapsulants of the present invention.

The laminates of the present invention may also be produced throughnon-autoclave processes. Such non-autoclave processes are disclosed, forexample, within U.S. Pat. Nos. 3,234,062; 3,852,136; 4,341,576;4,385,951; 4,398,979; 5,536,347; 5,853,516; 6,342,116; and 5,415,909, USPatent Application No. 2004/0182493, European Patent No. EP 1 235 683B1, and PCT Patent Application Nos. WO 91/01880 and WO 03/057478 A1.Generally, the non-autoclave processes include heating the laminateassembly or the pre-press assembly and the application of vacuum,pressure or both. For example, the pre-press may be successively passedthrough heating ovens and nip rolls.

If desired, the edges of the solar cell laminate may be sealed to reducemoisture and air intrusion and their potentially degradation effect onthe efficiency and lifetime of the solar cell by any means disclosedwithin the art. General art edge seal materials include, but are notlimited to, butyl rubber, polysulfide, silicone, polyurethane,polypropylene elastomers, polystyrene elastomers, block elastomers,styrene-ethylene-butylene-styrene (SEBS), and the like.

EXAMPLES

The following Examples are intended to be illustrative of the presentinvention, and are not intended in any way to limit the scope of thepresent invention. The solar cell interconnections are omitted from theexamples below to clarify the structures, but any common art solar cellinterconnections may be utilized within the present invention.

Methods

The following methods are used in the Examples presented hereafter.

I. Lamination Process 1:

The laminate layers described below are stacked (laid up) to form thepre-laminate structures described within the examples. For the laminatecontaining a film layer as the incident or back-sheet layer, a coverglass sheet is placed over the film layer. The pre-laminate structure isthen placed within a vacuum bag, the vacuum bag is sealed and a vacuumis applied to remove the air from the vacuum bag. The bag is placed intoan oven and while maintaining the application of the vacuum to thevacuum bag, the vacuum bag is heated at 135° C. for 30 minutes. Thevacuum bag is then removed from the oven and allowed to cool to roomtemperature (25±5° C.). The laminate is then removed from the vacuum bagafter the vacuum is discontinued.

II. Lamination Process 2:

The laminate layers described below are stacked (laid up) to form thepre-laminate structures described within the examples. For the laminatecontaining a film layer as the incident or back-sheet layer, a coverglass sheet is placed over the film layer. The pre-laminate structure isthen placed within a vacuum bag, the vacuum bag is sealed and a vacuumis applied to remove the air from the vacuum bag. The bag is placed intoan oven and heated to 90-100° C. for 30 minutes to remove any aircontained between the assembly. The pre-press assembly is then subjectedto autoclaving at 135° C. for 30 minutes in an air autoclave to apressure of 200 psig (14.3 bar), as described above. The air is thencooled while no more air is added to the autoclave. After 20 minutes ofcooling when the air temperature reaches less than about 50° C., theexcess pressure is vented, and the laminate is removed from theautoclave.

Examples 1-14

The 12-inch by 12-inch solar cell laminate structures described below inTable 1 are assembled and laminated by Lamination Process 1. In eachconstruct, the layers are described in the order of from top to bottomand the poly(vinyl butyral) sub-layer of the preformed bi-layer sheet isin direct contact with the solar cell surface.

TABLE 1 Solar Cell Laminate Structures Example Layer 1 Layer 2 Layer 3Layer 4 Layer 5  1, 15 Glass 1 PVB Solar Cell 1 Bilayer 1  2, 16 FPF EBASolar Cell 2 Bilayer 2  3, 17 Bilayer 3 Solar Cell 3 Bilayer 2  4, 18Glass 2 Ionomer 1 Solar Cell 4 Bilayer 1  5, 19 FPF EMA Solar Cell 1Bilayer 2  6, 20 Bilayer 3 Solar Cell 1 ACR AL  7, 21 Glass 3 EVA SolarCell 4 Bilayer 2  8, 22 Bilayer 3 Solar Cell 1 PVB A AL  9, 23 Glass 1Ionomer 2 Solar Cell 4 Bilayer 2 10, 24 Glass 2 PVB Bilayer 2 Solar CellBilayer 1 2 11, 25 Bilayer 3 Solar Cell 4 Bilayer 2 ACR AL 12, 26Bilayer 3 Solar Cell 1 Bilayer 3 13, 27 Bilayer 3 Solar Cell 2 Ionomer 1Glass 1 14, 28 Bilayer 3 Solar Cell 3 PVB A Glass 2 ACR is a 20 mil(0.51 mm) thick embossed sheet of a poly(ethylene-co-methacrylic acid)containing 15 wt % of polymerized residues of methacrylic acid andhaving a MI of 5.0 g/10 minutes (190° C., ISO 1133, ASTM D1238). AL isan aluminum sheet (3.2 mm thick) and is 5052 alloyed with 2.5 wt % ofmagnesium and conforms to Federal specification QQ-A-250/8 and ASTMB209. Bilayer 1 is SentryGlas ® Spallshield 3010, a product of DuPont.Bilayer 2 is SentryGlas ® Spallshield 1510, a product of DuPont. Bilayer3 is a bi-laminate of a corona surface treated Tedlar ® film gradeWH15BL3 (1.5 mil (0.038 mm) thick), a product of DuPont, and a 20 mil(0.51 mm) thick plasticized poly(vinyl butyral) sheet. EBA is aformulated composition based on poly(ethylene-co-butyl acrylate)containing 20 wt % of polymerized residues of butyl acrylate based onthe total weight of the copolymer and in the form of a 20 mil (0.51 mm)thick sheet. EMA is a formulated composition based onpoly(ethylene-co-methyl acrylate) containing 20 wt % of polymerizedresidues of methyl acrylate based on the total weight of the copolymerand in the form of a 20 mil (0.51 mm) thick sheet. EVA is SC50B,believed to be a formulated composition based on poly(ethylene-co-vinylacetate) in the form of a 20 mil (0.51 mm) thick sheet (a product of theHi-Sheet Corporation, formerly Mitsui Chemicals Fabro, Inc.). FPF is acorona surface treated Tedlar ® film grade WH15BL3 (1.5 mil (0.038 mm)thick), a product of DuPont. Glass 1 is Starphire ® glass from the PPGCorporation. Glass 2 is a clear annealed float glass plate layer (2.5 mmthick). Glass 3 in a Solex ® solar control glass (3.0 mm thick). Ionomer1 is a 90 mil (2.25 mm) thick embossed sheet of apoly(ethylene-co-methacrylic acid) containing 18 wt % of polymerizedresidues of methacrylic acid that is 30% neutralized with zinc ion andhaving a MI of 1 g/10 minutes (190° C., ISO 1133, ASTM D1238). Ionomer 1is prepared from a poly(ethylene-co-methacrylic acid) having a MI of 60g/10 minutes. Ionomer 2 is a 20 mil (0.51 mm) thick embossed sheet of apoly(ethylene-co-methacrylic acid) containing 22 wt % of polymerizedresidues of methacrylic acid that is 26% neutralized with zinc ion andhaving a MI of 0.75 g/10 minutes (190° C., ISO 1133, ASTM D1238).Ionomer 2 is prepared from a poly(ethylene-co-methacrylic acid) having aMI of 60 g/10 minutes. PVB is B51V, believed to be a formulatedcomposition based on poly(vinyl butyral) in the form of a 20 mil (0.51mm) thick sheet (a product of DuPont) PVB A is an acoustic poly(vinylbutyral) sheet including 100 parts per hundred (pph) poly(vinyl butyral)with a hydroxyl number of 15 plasticized with 48.5 pph plasticizertetraethylene glycol diheptanoate prepared similarly to disclosed withinPCT Patent Application No. WO 2004/039581. Solar Cell 1 is a 10-inch by10-inch amorphous silicon photovoltaic device comprising a stainlesssteel substrate (125 micrometers thick) with an amorphous siliconsemiconductor layer (U.S. Pat. No. 6,093,581, Example 1). Solar Cell 2is a 10-inch by 10-inch copper indium diselenide (CIS) photovoltaicdevice (U.S. Pat. No. 6,353,042, column 6, line 19). Solar Cell 3 is a10-inch by 10-inch cadmium telluride (CdTe) photovoltaic device (U.S.Pat. No. 6,353,042, column 6, line 49). Solar Cell 4 is a silicon solarcell made from a 10-inch by 10-inch polycrystalline EFG-grown wafer(U.S. Pat. No. 6,660,930, column 7, line 61).

Examples 15-28

The 12-inch by 12-inch solar cell laminate structures described above inTable 1 are assembled and laminated by Lamination Process 2. In eachconstruct, the layers are described in the order of from top to bottomand the poly(vinyl butyral) sub-layer of the preformed bi-layer sheet isin direct contact with the solar cell surface.

1. A solar cell laminate comprising (i) a solar cell layer comprisingone or a plurality of electronically interconnected solar cells andhaving a light-receiving side and a back side, and (ii) at least onepreformed bi-layer sheet comprising a first sub-layer comprising apoly(vinyl butyral) and a second sub-layer comprising a metal orpolymeric film.
 2. The solar cell laminate of claim 1, wherein saidmetal film is an aluminum foil.
 3. The solar cell laminate of claim 1,wherein said polymeric film comprises a polymeric composition selectedfrom the group consisting of poly(ethylene terephthalate),polycarbonate, polypropylene, polyethylene, polypropylene, cyclicpolyolefins, norbornene polymers, polystyrene, syndiotactic polystyrene,styrene-acrylate copolymers, acrylonitrile-styrene copolymers,poly(ethylene naphthalate), polyethersulfone, polysulfone, nylons,poly(urethanes), acrylics, cellulose acetates, cellulose triacetates,cellophane, vinyl chloride polymers, polyvinylidene chloride, vinylidenechloride copolymers, fluoropolymers, polyvinyl fluoride, polyvinylidenefluoride, polytetrafluoroethylene, and ethylene-tetrafluoroethylenecopolymers.
 4. The solar cell laminate of claim 1, wherein said one or aplurality of solar cells are selected from the group consisting ofmulti-crystalline solar cells, thin film solar cells, compoundsemiconductor solar cells, and amorphous silicon solar cells.
 5. Thesolar cell laminate of claim 1, wherein said at least one preformedbi-layer sheet is laminated to the light-receiving side of said solarcell layer and serves as a front-sheet encapsulant layer, and whereinthe second sub-layer of said at least one preformed bi-layer sheetcomprises said polymeric film.
 6. The solar cell laminate of claim 5,further comprising a back-sheet encapsulant layer that is laminated tothe back side of said solar cell layer and comprises a polymericcomposition selected from the group consisting of poly(vinyl butyral),ionomers, ethylene vinyl acetate, acoustic poly(vinyl acetal), acousticpoly(vinyl butyral), thermoplastic polyurethane, polyvinylchloride,metallocene-catalyzed linear low density polyethylenes, polyolefin blockelastomers, ethylene acrylate ester copolymers, acid copolymers,silicone elastomers and epoxy resins.
 7. The solar cell laminate ofclaim 6, wherein said back-sheet encapsulant layer is formed of a secondpreformed bi-layer sheet.
 8. The solar cell laminate of claim 1, whereinsaid at least one preformed bi-layer sheet is laminated to the back sideof said solar cell layer and serves as a back-sheet encapsulant layer.9. The solar cell laminate of claim 8, further comprising a front-sheetencapsulant layer that is laminated to the light-receiving side of saidsolar cell layer and comprises a polymeric composition selected from thegroup consisting of poly(vinyl butyral), ionomers, ethylene vinylacetate, acoustic poly(vinyl acetal), acoustic poly(vinyl butyral),thermoplastic polyurethane, polyvinylchloride, metallocene-catalyzedlinear low density polyethylenes, polyolefin block elastomers, ethyleneacrylate ester copolymers, acid copolymers, silicone elastomers andepoxy resins.
 10. The solar cell laminate of claim 6, wherein the firstsub-layer of said at least one preformed bi-layer sheet is in directcontact with and adhered to said solar cell layer.
 11. The solar celllaminate of claim 10, wherein the second sub-layer of said at least onepreformed bi-layer sheet has at least one side hard coated.
 12. Thesolar cell laminate of claim 10, further comprising a back-sheetlaminated to said back-sheet encapsulant layer opposite from said solarcell layer.
 13. The solar cell laminate of claim 10, further comprisingan incident layer and a second front-sheet encapsulant layer, whereinsaid incident layer is bonded to said preformed bi-layer sheet with saidsecond front-sheet encapsulant layer in between.
 14. The solar celllaminate of claim 9, wherein the first sub-layer of said at least onepreformed bi-layer sheet is in direct contact with and adhered to saidsolar cell layer.
 15. The solar cell laminate of claim 14, wherein thesecond sub-layer of said at least one preformed bi-layer sheet has atleast one side hard coated.
 16. The solar cell laminate of claim 14,further comprising an incident layer laminated to said front-sheetencapsulant layer opposite from said solar cell layer.
 17. The solarcell laminate of claim 14, further comprising a back-sheet and a secondback-sheet encapsulant layer, wherein said back-sheet is bonded to saidat least one preformed bi-layer sheet with said second back-sheetencapsulant layer in between.
 18. The solar cell laminate of claim 6,further comprising a second front-sheet encapsulant layer, wherein thesecond sub-layer of said at least one preformed bi-layer sheet is indirect contact with and adhered to said second front-sheet encapsulantlayer, which is in turn in direct contact with and adhered to thelight-receiving side of said solar cell layer.
 19. The solar celllaminate of claim 18, further comprising an incident layer laminated tosaid at least one preformed bi-layer sheet at the first sub-layer sideand a back layer laminated to said back-sheet encapsulant layer oppositefrom said solar cell layer.
 20. The solar cell laminate of claim 9,further comprising a second back-sheet encapsulant layer, wherein thesecond sub-layer of said at least one preformed bi-layer sheet is indirect contact with and adhered to said second back-sheet encapsulantlayer, which is in turn in direct contact with and adhered to the backside of said solar cell layer.
 21. The solar cell laminate of claim 20,further comprising an incident layer laminated to said front-sheetencapsulant layer opposite from said solar cell layer and a back-sheetlaminated to said at least one preformed bi-layer sheet at the firstsub-layer side.
 22. A process of manufacturing a solar cell laminatecomprising: (i) providing an assembly comprising, from top to bottom, afront-sheet encapsulant layer, a solar cell layer comprising one or aplurality of electronically interconnected solar cells, and a back-sheetencapsulant layer, and (ii) laminating the assembly to form the solarcell module, wherein at least one of the two encapsulant layers isformed of a preformed bi-layer sheet comprising a first sub-layercomprising a poly(vinyl butyral) and a second sub-layer comprising ametal or polymeric film.
 23. The process of claim 22, wherein saidfront-sheet encapsulant layer is formed of said preformed bi-layer sheetwith its first sub-layer in direct contact with said solar cell layer,and wherein said assembly in step (i) further comprises a back-sheetplaced next to said back-sheet encapsulant layer opposite from saidsolar cell layer.
 24. The process of claim 23, wherein said assembly instep (i) further comprises a second front-sheet encapsulant layer and anincident layer, wherein said incident layer is placed next to saidsecond front-sheet encapsulant layer, which in turn is in direct contactwith the second sub-layer of said preformed bi-layer sheet.
 25. Theprocess of claim 22, wherein said back-sheet encapsulant layer is formedof said preformed bi-layer sheet with its first sub-layer in directcontact with said solar cell layer, and wherein said assembly in step(i) further comprises an incident layer placed next to said front-sheetencapsulant layer opposite from said solar cell layer.
 26. The processof claim 25, wherein said assembly in step (i) further comprises asecond back-sheet encapsulant layer and a back-sheet, wherein saidback-sheet is placed next to said second back-sheet encapsulant layer,which in turn is in direct contact with the second sub-layer of saidpreformed bi-layer sheet.
 27. The process of claim 22, wherein saidfront-sheet encapsulant layer is formed of said preformed bi-layer sheetwith its second sub-layer in a closer proximity to said solar celllayer; wherein said assembly in step (i) further comprises an incidentlayer, a second front-sheet encapsulant layer, and a back-sheet; whereinsaid incident layer is placed next to the first sub-layer of saidpreformed bi-layer sheet, which in turn has its second sub-layer indirect contact with said second front-sheet encapsulant layer, and whichin turn is in direct contact with said solar cell layer; and whereinsaid back-sheet is placed next to said back-sheet encapsulant layeropposite from said solar cell layer.
 28. The process of claim 22,wherein said back-sheet encapsulant layer is formed of said preformedbi-layer sheet with its second sub-layer in a closer proximity to saidsolar cell layer; wherein said assembly in step (i) further comprises anincident layer, a second back-sheet encapsulant layer, and a back-sheet;wherein said incident layer is placed next to said front-sheetencapsulant layer opposite from said solar cell layer; and wherein saidback-sheet is placed next to the first sub-layer of said preformedbi-layer sheet, which in turn has its second sub-layer in direct contactwith said second back-sheet encapsulant layer, and which in turn is indirect contact with said solar cell layer.
 29. The process of claim 22,wherein the step (ii) of lamination is conducted by subjecting theassembly to heat.
 30. The process of claim 29, wherein the step (ii) oflamination further comprises subjecting the assembly to pressure. 31.The process of claim 29, wherein the step (ii) of lamination furthercomprises subjecting the assembly to vacuum.